The invention relates to surface preparation of a workpiece, such as silicon or gallium arsenide wafers, flat panel displays, mask reticles, rigid disk media, thin film heads, or other substrates on which electronic, optical, or micro-mechanical components have or can be formed, collectively referred to here singly as a xe2x80x9cworkpiecexe2x80x9d.
Surface preparation, such as cleaning, etching, and stripping, is an essential and important element of the manufacturing process for semiconductor wafers and similar workpieces. Surface preparation steps are commonly performed, using liquid corrosive, caustic, or solvent chemicals, or using vapor phase chemicals. Surface preparation of workpieces is performed to prepare or condition the surface for a subsequent process step.
Cleaning is a critical step in manufacturing semiconductors and similar products. Cleaning involves the use of chemical formulations to remove contaminants, such as oxides, particles, metals, or organic material, while maintaining the cleanliness and integrity of the surface of the workpiece. Some liquid, gas or vapor phase chemicals when applied to a workpiece, result in surface characteristics that are more susceptible to contamination than others. For example, application of hydrofluoric acid (HF) to the surface of a workpiece will remove oxide from the silicon surface, resulting in a surface that is active. Workpieces in general, and especially workpieces having an active surface, are constantly susceptible to contamination by airborne microscopic particles. Contamination can also occur in the cleaning process, when the liquid process media is removed from the surface of the workpiece.
Thus, to minimize contamination of the workpiece, it is advantageous to perform a sequence of surface preparation steps within a controlled environment, that preferably occupies a relatively small amount of fabrication facility space, and in which exposure to contamination sources is minimized. Accordingly, it is an object of the invention to provide improved surface processing methods and apparatus.
Cleaning workpieces while avoiding or minimizing contamination has long been an engineering challenge. Workpieces are often cleaned with a spray or bath of de-ionized water. The water is then removed, often in the presence of an organic solvent vapor, such as isopropyl alcohol, which lowers the surface tension of the water. This helps to prevent droplets of water from remaining on and contaminating the workpiece.
Various cleaning methods and systems and various rinsing and drying methods and apparatus have been proposed and used. In a typical system, wafers are immersed in a vessel. A mechanism is provided to hold the wafers. Another mechanism is provided to lift the wafers out of the liquid, by pushing them up from below. While this technique has been used, it can result in trapping of liquid in or around the spaces where the wafers contact the holding mechanism, resulting in increased contamination. It is also complicated by the need for the lifting mechanism. In an alternative system, the wafers are held in a fixed position while the liquid is drained away from below. This technique has less tendency for trapping liquid. However, as the liquid level drops, the solvent vapor above the liquid is absorbed by the liquid. Consequently, the top sections of the wafer are exposed to liquid which is different from the liquid at the bottom sections of the wafers. This potentially results in non-uniform processing. Accordingly, while these and other techniques have been used with varying degrees of success, there is still a great need for improved systems and methods for cleaning workpieces.
It is therefore also an object of the invention to provide an improved system and method for cleaning workpieces.
To this end, in a first aspect, surface preparation processes on a workpiece or workpieces are performed within a single apparatus. This minimizes exposure of the workpiece to contaminants and provides an improved application of process fluids or media to the workpiece.
In a second aspect, an apparatus has a rotor rotatably supported within a process chamber. The process chamber can pivot to move a drain outlet in the process chamber down to the level of the liquid contained in the chamber. The liquid then drains out of the chamber through the outlet. The process chamber provides for containment of process fluid. An optional second or outer containment chamber provides for containment and disposal of process fluid, and for isolating the process environment from the ambient environment, human operators, and adjacent parts and equipment. This minimizes exposure of the workpiece to contaminants and provides an improved application of process fluids or media to the workpiece.
In a third aspect, an inner chamber has a drain opening to allow process fluid to be removed from the inner process chamber. A drive motor pivots the inner process chamber at a controlled rate to bring and then maintain the opening at or below the level of the fluid in the inner chamber. The fluid then drains out from the drain opening. The drive motor may move the inner process chamber by magnetic forces, without an actual physical penetration of or connection into the process environment by a drive shaft. Optionally, the inner process chamber may be connected to the drive motor with a drive shaft, with a shaft seal sealing the shaft opening into the inner process chamber.
In a fourth aspect, the inner process chamber forms a closed chamber, without any drain opening. The workpieces remain stationary, during at least one process step, and a drive motor spins the inner process chamber around the stationary workpieces. Openings or spray nozzles on or in the inner process chamber supply a fluid onto the workpieces. To remove liquid from the chamber, the chamber is turned to or braked to a stop at a position where one or more drain ports are at a bottom position. The drain ports are then opened and the liquid drains out through them via gravity. A gas may be provided into the inner process chamber during draining, to prevent creation of a vacuum slowing or stopping the out flow of liquid. Liquid may alternatively be removed by opening the drain ports and then positioning and maintaining the drain ports at or below the liquid surface by slowly pivoting the inner process chamber, as in the third aspect described above. This allows for controlled removal of liquid, resulting is less potential for contamination of the workpieces.
In a fifth aspect, the inner chamber is closed or sealed and remains stationary and the workpieces spin within the inner chamber. This minimizes exposure of the workpiece to contaminants and provides an improved application of process fluids to the workpiece.
In a sixth aspect, sonic energy, such as ultrasonic or megasonic energy, is applied to the workpiece, preferably through liquid in which the workpiece is immersed. This improves processing as the sonic energy contributes to the processing along with the chemical reactions of the process liquids.
In a seventh aspect, the outer containment chamber is purged with a gas and/or vapor to maintain a desired environment around the workpiece. The gas or vapor may be nitrogen, or argon, or hydrofluoric acid (HF).
In an eigth aspect, unique methods for cleaning a workpiece are provided. These methods solve the problems of the known methods now used in the semiconductor manufacturing industry. Workpieces are held in a rotor within a process chamber having a drain outlet or slot. The workpieces are immersed in liquid within the process chamber. Liquid is preferably continuously supplied into the chamber so that liquid is continuously overflowing and running out of the drain outlet. The process chamber is pivoted to move the drain outlet down in a controlled movement, to lower the level of liquid in the chamber. Liquid supply to the chamber and overflow at the liquid surface preferably continues as the chamber pivots and the liquid level drops. This process continues until the liquid level drops below the workpieces and the chamber is pivoted to drain virtually all liquid out of the chamber.
By maintaining the overflow at the liquid surface, and by maintaining a constant flow towards and out of the drain outlet, impurities at the liquid surface flow away from the workpieces, reducing potential for contamination. The liquid in the chamber remains uniform at all depths, as the surface of the liquid which the solvent vapor dissolves into, is constantly being replaced with fresh liquid. After the liquid is removed from the chamber, the workpieces are advantageously rotated. Liquid droplets remaining on the workpieces or adjacent components of the apparatus are centrifugally removed. Consequently, cleaning is provided with a uniform liquid bath and with reduced potential for trapped or residual liquid remaining on the workpieces. The disadvantages associated with the machines and methods currently in use, as described above, are overcome.
The aspects of the invention described above provide greatly improved processing and cleaning apparatus and methods. These aspects help to provide more reliable and efficient processing.
Further embodiments and modifications, variations and enhancements of the invention will become apparent. The invention resides as well in subcombinations of the features shown and described. Features shown in one embodiment may also be used in other embodiments as well.